This invention relates to an improvement in a nuclear fuel conversion system for obtaining uranium dioxide, plutonium dioxide, or a mixture thereof from a nitric acid solution of uranyl nitrate, plutonium nitrate, or a mixture thereof.
A nuclear fuel conversion system of this type generally comprises a denitrification unit for denitrifying a nitric acid solution, a roast-reduction unit for roasting and reducing a denitrified product, a unit for grinding and sieving the roasted and reduced product, a waste disposal unit for disposing of waste gases and waste liquor exhausted from the units described above, and conveying means for conveying products produced by one unit to the succeeding unit.
However, in the nuclear fuel conversion system of the known type described above, the denitrification unit generally has a complicated construction which results in an inconvenience of maintenance or operation. This is because the denitrification unit utilizes a precipitation method and a sol-gel process as part of a complicated wet denitrification method and a method utilizing a fluidized bed as part of a thermal decomposition process for a dry denitrification method.
For example, in a conventional direct denitrification method utilizing a fluidized bed, in which a plutonium-uranium mixture solution is sprayed onto a fluidized bed, then roasted, and reduced, thereby to convert the solution to a dioxide, disadvantages occur in that the quality of the final product, dioxide, is not good the, waste gas contains nitrogen oxides (NOx), and a good decontamination factor (DF) of an impurity can not be expected.
An ammonia coprecipitation method of a known type in which ammonia is added to the plutonium-uranium mixture solution and the precipitate produced is filtered, dried, roasted and reduced so as to obtain a converted dioxide, includes such disadvantages as that the precipitate is not completely removed by the filtration, and a good DF is not expected so that the process as a whole is considerably complicated.
Moreover, a direct denitrification method utilizing microwave energy to heat a nitric acid solution in a denitrification process has been proposed. However, this denitrification method also has the disadvantages that the waste gas contains NOx and a good DF is not expected.
Furthermore, in the known methods or apparatus, intermediate products produced by the respective units of the nuclear fuel conversion system are conveyed by means of conveyers such as conveyor belts or by sealing them in containers, which complicates the conveying means and creates a fear of leaking or scattering of the products during transportion.